Every October our phones start ringing with the same story: the first real cold snap hits St. Charles County, the space heaters come out of the closet, and a breaker somewhere starts tripping. Winter heating puts more strain on a home's electrical system than anything else it does all year. This is how those loads actually add up, and how to get ahead of them before the first hard freeze.
Understanding Heating Electrical Loads
Electric Resistance Heat
Baseboard heaters: - 250W per linear foot typical - 8-foot heater = 2,000W - Entire home system: 10,000-25,000W
Electric furnace: - Uses resistance heating elements - 10,000-25,000W typical - All-electric homes: Major electrical load
Heating element fact: 1,500W space heater = 1,500W baseboard = 1,500W wall heater. The delivery method differs, but electrical demand is the same.
Heat Pumps
More efficient than resistance heat: - Uses ~1W electricity to move 2-4W of heat - Typical heat pump: 3,000-6,000W - Much lower than equivalent resistance heat
Backup heat (emergency/auxiliary): - Electric strips for extreme cold - Adds 5,000-15,000W when active - Triggers when temperature differential is large
Supplemental Heating
Space heaters: - Standard: 1,500W (max for 120V outlet) - Small: 750W - Each requires significant circuit capacity
Electric blankets/mattress pads: - 200-400W typical - Much more efficient than heating whole room
Circuit Capacity Challenges
The Math Problem
Standard bedroom circuit: 15 amps — that's 1,800W peak, but code treats anything running 3+ hours (like a heater) as a continuous load, which caps the safe number at 1,440W.
Typical winter morning load: - Space heater: 1,500W - Desk lamp: 10W - Phone charger: 20W - TV: 100W - Total: 1,630W — already past the 1,440W continuous rating. That circuit is living on borrowed time, and anything else (hair dryer, vacuum, second heater) trips it.
Space Heater Rules
Critical requirements: 1. One heater per circuit maximum 2. Never use extension cords 3. Plug directly into wall outlet 4. Check outlet for warmth periodically
Why extension cords are dangerous: - Not rated for continuous high loads - Connections can overheat - Wire gauge often insufficient - Fire hazard
Circuit Sharing Solutions
Option 1: Dedicated circuits - Run new circuits for heavy heating loads - 20-amp circuit per 1,500W heater - Most reliable solution
Option 2: Load management - Don't run multiple heaters on same circuit - Alternate usage between rooms - Use central heating as primary
Option 3: Circuit identification - Map which outlets share circuits - Place heaters on separate circuits - Post reminder near heaters
Schedule dedicated circuit installation
Heat Pump Considerations
Electrical Requirements
Heat pump electrical needs: - Outdoor unit: 240V, 20-40 amp circuit - Air handler: May share or need separate circuit - Control wiring: Low voltage to thermostat
Auxiliary Heat Impact
When aux heat activates: - Electrical demand can triple or quadruple - May cause momentary dimming - Places strain on panel capacity
Minimize aux heat: - Don't set thermostat back more than 2-3 degrees - Use "Emergency Heat" setting only for actual emergencies - Maintain moderate, consistent temperatures
Cold Weather Performance
Heat pump efficiency vs temperature: - Above 40°F: Maximum efficiency - 25-40°F: Good efficiency - Below 25°F: Efficiency drops, aux heat may help - Below 10°F: Heavy aux heat reliance
Modern cold-climate heat pumps: - Maintain efficiency to lower temperatures - Reduce need for aux heat - May need panel upgrade for higher capacity
Panel Capacity Planning
Signs of Capacity Issues
Warning signs during heating season: - Breakers trip when heat kicks on - Lights dim when heater activates - Panel warm to touch - Burning smell from panel
These require immediate attention. Call an electrician.
Load Calculation
Basic calculation method:
| Load | Wattage |
|---|---|
| Heating system | 5,000-25,000W |
| Water heater | 4,500W |
| Electric dryer | 5,000W |
| Electric range | 8,000-12,000W |
| AC (summer) | 3,000-6,000W |
| Other circuits | 3,000-5,000W |
Total potential load: 25,000-50,000W+
100-amp panel capacity: ~24,000W 200-amp panel capacity: ~48,000W
If your loads exceed panel capacity, you need load management or panel upgrade.
Load Management Options
Smart panels (Span, Lumin): - Automatic load prioritization - Prevent overloads intelligently - May avoid need for panel upgrade
Manual management: - Don't run all heavy loads simultaneously - Schedule water heater for off-peak - Alternate space heater locations
Energy Efficiency Strategies
Reduce Heating Load
Before running more electric heat: - Seal air leaks around outlets and switches - Insulate attic access doors - Address drafty windows and doors - Verify adequate insulation
Energy saved = electricity not needed.
Zone Heating
Smart heating approach: - Heat occupied rooms to comfort - Allow unoccupied rooms to be cooler - Use programmable thermostats - Close vents/doors to unused spaces
Zone heating can reduce costs 10-30%.
Time-of-Use Optimization
If on time-of-use rates: - Pre-heat home during off-peak hours - Use thermal mass of house to coast through peaks - Schedule water heater for overnight - Delay laundry until off-peak
Smart Thermostat Benefits
Features that save energy: - Learning your schedule - Geofencing (away detection) - Optimal start times - Energy usage reports - Integration with utility programs
Space Heater Best Practices
Safety Guidelines
Placement: - 3 feet from anything combustible - On floor (not table or shelf) - Away from foot traffic - Never in bathroom with water exposure
Operation: - Turn off when leaving room - Turn off when sleeping - Never cover or obstruct - Verify tip-over switch works
Efficient Use
Maximize effectiveness: - Close doors to heated room - Direct heat toward occupied area - Use timer to avoid overnight operation - Choose right size for space
When space heaters make sense: - Supplementing inadequate central heat - Heating single occupied room - Temporary need (room addition, broken furnace)
When central heat is better: - Whole-home heating needs - Long-term use - Multiple rooms simultaneously
Warning Signs to Watch
Call an Electrician If:
- Breakers trip repeatedly during heating season
- Outlets feel warm with heaters plugged in
- Burning smell from outlets or panel
- Lights dim significantly when heat activates
- Scorch marks near outlets
Schedule Service For:
- Panel at or near capacity
- Planning to add heating equipment
- Old wiring (knob-and-tube, aluminum)
- Frequent breaker trips
- Questions about circuit capacity
Not sure your panel can carry another St. Louis winter? We do this walkthrough all season — map your circuits, check the panel under load, and tell you honestly whether you need new circuits or just a better plan for the heaters you already own. Schedule an assessment before the first hard freeze.